Process for preparing low haze, high temperature-resistant laminates

ABSTRACT

A process for providing a low haze, high transparent, high heat-resistant laminate by forming a preform laminate of a high heat-resistant layer covered on both surfaces by a non-glass protective layer with at least one said layer being an as-cast acrylic layer. This combination can be readily stored for long periods of time or used immediately after the formation thereof by peeling off one of the as-cast acrylic layers and applying a transparent flexible adhesive layer thereto. The transparent material can be added to the adhesive layer. Many other combinations and laminates can be formed from the preform high heat-resistant laminate since during the preparation thereof, haze is not introduced to the transparency via moisture, and contact with haze-forming release coatings is avoided.

CROSS-REFERENCE

This application is a continuation-in-part of U.S. Ser. No. 232,054filed Feb. 5, 1981, now U.S. Pat. No. 4,343,928 which in turn is acontinuation-in-part application of an application filed on Aug. 28,1979, bearing Ser. No. 70,390, now U.S. Pat. No. 4,294,886. Thisapplication is also a continuation-in-part application of U.S. Ser. No.232,054, filed Feb. 5, 1981, now U.S. Pat. No. 4,543,928, which in turnis a continuation-in-part application of an application filed on Nov. 6,1980, bearing Ser. No. 204,424, now U.S. Pat. No. 4,352,848. ApplicationSer. No. 204,424 is a continuation-in-part of application Ser. No.70,390, filed Aug. 28, 1979 now U.S. Pat. No. 4,294,886.

TECHNICAL FIELD

The present invention relates to a process for the preparation of highheat-resistant transparencies and laminates thereof having low haze. Theprocess eliminates contact with haze-forming compounds as well asprevents moisture contact which will result in haze formation. Numeroushigh heat-resistant laminates can be produced by the present invention.

BACKGROUND ART

Heretofore, no known prior art existed.

My above-noted copending specifications relate to the forming of alaminate having a glass layer, a space between said glass layer and anas-cast acrylic layer, and a glass layer on the other side of saidas-cast acrylic layer. A high heat-resistant material would then be castinto the space. In order to prevent adhesion between the highheat-resistant material and the glass, various release agents such asRepcon, a trademark of Unelko Corporation, Chicago, Ill., containingtetraethylorthosilicate, was applied to the glass. However, such releasecoatings would often adhere to the high heat-resistant layer and imparta haze thereto. Moreover, upon removal of the glass layer, and prior tosubsequent application of a transparent material thereon, moisture wouldcommence buildup which would also impart haze to the high heat-resistantlayer. Although such layer could be heated in an oven prior to theapplication of a layer thereon, not all of the moisture was removed andthus some haze still remained. The laminate could be applied incombination with other transparent layers to form any number ofcombinations of various laminates, all having high heat resistance.However, the final product or laminate was not as haze-free as oftendesired.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide a processfor forming high heat-resistant laminates having low haze values.

It is another object of the present invention to provide a process formaking high heat-resistant, low haze laminates, as above, wherein a highheat-resistant material is located between a pair of as-cast acryliclayers or between one acrylic layer and a non-glass transparent materiallayer.

It is yet another object of the present invention to provide a processfor making high heat-resistant, low haze laminates, as above, whereinsaid process eliminates the use of any release agents.

It is another object of the present invention to provide a process formaking high heat-resistant, low haze laminates, as above, wherein saidhigh heat-resistant layer sandwiched between said non-glass layers, atleast one of which is an as-cast acrylic layer which can be stored foran indefinite period of time and is generally resistant to moisture.

It is yet another object of the present invention to provide a processfor making high heat-resistant, low haze laminates, as above, wherein anas-cast acrylic layer is removed from said high heat-resistant layerwith the subsequent item combined with at least another layer ofmaterial to form various laminates.

It is yet another object of the present invention to provide a processfor making high heat-resistant, low haze laminates, as above, whereinsaid various steps can be carried out at various temperatures utilizingvarious specific materials.

These and other objects of the present invention will become moreapparent from the detailed description of the preferred embodiment.

In general, a process for preparing a transparent, low haze, highheat-resistant laminate, comprises the steps of: forming a highheat-resistant layer, said high heat-resistant layer having atransparent protective layer on either side thereof, at least one ofsaid protective layers being an as-cast acrylic layer.

Additionally, a process for preparing a transparent, low haze,heat-resistant laminate, comprises the steps of: locating two protectivelayers in juxtaposition to one another and having a space therebetween,at least one of said protective layers being an as-cast acrylicmaterial; locating a glass layer on each acrylic layer; and adding ahigh heat-resistant material between said spaced protective layers.

BRIEF DESCRIPTION OF DRAWINGS

For an understanding of the invention, reference is had to the followingdrawings, wherein:

FIG. 1 is a cross-sectional view of the transparency composite havingthe intense heat-resistant layer;

FIG. 2 is a cross-sectional view of the clad transparency compositehaving the intense heat-resistant interlayer;

FIG. 3 is a graph of the production of the transparency having benzylalcohol showing the increase in gel time;

FIG. 4 is a graph showing the effect of alcohol levels on the maximumexotherm in the reaction system;

FIG. 5 is a graph showing the increased burn-through resistance on thetransparencies having benzyl alcohol and triphenyl phosphite;

FIG. 6 is a graph showing the increased resistance to moisturepermeability of mercaptan resin binding means bonded to varioustransparency layers when exposed to temperatures of about 200° F. and100 percent relative humidity;

FIG. 7 is a graph showing the increased resistance to moisturepermeability of mercaptan resin binding means bonded to varioustransparency layers when exposed to temperatures of about 120° F. and 95percent relative humidity;

FIG. 8 is a graph showing the increased resistance to moisturepermeability of mercaptan resin binding means bonded to other varioustransparency layers when exposed to temperatures of about 200° F. and100 percent relative humidity;

FIG. 9 is a graph showing the composite evaluation of various interlayerbinding means and the effectiveness of resistance to moisturepermeability;

FIG. 10 is a cross-sectional view of a transparency composite at an edgeas sealed by edge sealant material of the present invention;

FIG. 11 is a cross-sectional view of a transparency composite having noinnerlayer binding means between the intense heat-resistant interlayerand the outside ply;

FIG. 12 is an illustrative view of a transparency composite having aslot to be filled and an edge-sealant material;

FIG. 13 is a graph showing the variation in concentrations of theconcentrations of the composition of the present invention and itseffect on modulus stability during humidity exposure;

FIG. 14 is a graph showing the variation in concentrations of thecomposition of the present invention and its effect on ultimate strengthstability during humidity exposure;

FIG. 15 is a cross-sectional view of the transparency composite havingan intense heat-resistant interlayer having a chlorophosphate compound;

FIG. 16 is a graph showing the relationship between the concentration ofthe phosphate compound and the ability of the heat-resistant interlayerto resist flame penetration;

FIG. 17 is a cross-sectional view of an initial laminate of the presentinvention;

FIG. 18 is a cross-sectional view showing the laminate of FIG. 17 havingthe two outer layers removed;

FIG. 19 is a cross-sectional view showing the top layer of FIG. 18 beingremoved;

FIG. 20 is a cross-sectional view showing the remaining laminate of FIG.18 incorporated into a final laminate; and

FIG. 21 is a flow diagram briefly outlining some of the variousprocesses of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Transparencies that have been produced with epoxy resins desiring toachieve heat-resistant properties have typically included a boroxinesuch as trimethoxyboroxine. Typical epoxy resins include, but are notlimited to, bisphenol-A type, bisphenol-F type, and novalac type epoxyresins. Typical boroxines include boroxines having the formula ##STR1##where R is a group having from 1 or 2 to 18 carbon atoms. Desirably, Ris an alkyl group and has from 1 or 2 to 5 carbon atoms.Trimethoxyboroxine is preferred. Trimethoxyboroxine has exhibited, incombination with epoxy resin, a resistance to heat from a general orpoint source up to temperatures of 2,000° F. However, a majorcomplication is the low concentration of trimethoxyboroxine in the epoxyresin system. Previously, for large casting purposes, it was possible touse a concentration of trimethoxyboroxine of 5-7.5 parts per hundredparts of epoxy resin (PHR). Any greater concentration woulddeleteriously promote the reaction between the trimethoxyboroxine andepoxy resin, resulting in a short gel time making it extremelyimpractical to cast large panels.

It has been found that higher concentrations of a boroxine such astrimethoxyboroxine can be incorporated into an epoxy resin system andstill have sufficient time to cast large sheets if a phenyl substitutedalkyl alcohol is added. The alkyl alcohol contains from 1 to 20 carbonatoms and desirably from 1 to 10 carbon atoms. Preferably, benzylalcohol is used. The alcohol acts as retarder and inhibitor for thetrimethoxyboroxine epoxy reaction, permitting the usage of an increasedconcentration of the trimethoxyboroxine and a concommitant increase inheat resistant properties. This concentration may be readily increasedto 30 parts of a boroxine such as trimethoxyboroxine per hundred partsof epoxy resin. Not only is the rate of reaction between thetrimethoxyboroxine and epoxy resins inhibited, but the maximum exothermis significantly reduced with the phenyl substituted alkyl alcoholaddition, as shown in FIG. 4.

                  TABLE 1                                                         ______________________________________                                        THE EFFECT OF BENZYL ALCOHOL                                                  ON MAXIMUM EXOTHERM                                                                          Curve                                                                         2       3      4                                               ______________________________________                                        Trimethoxyboroxine                                                                             10        10     10                                          Benzyl Alcohol    2         3      4                                          Dow DEN-431      85        85     85                                          Neopentyl Glycol                                                              Diglycidyl Ether 15        15     15                                          Gel Time (Minutes)                                                                             65        85     No sharp                                                                      gel time                                    Maximum Exotherm (°F.)                                                                  270       215    115                                         ______________________________________                                    

While phenyl substituted alkyl alcohols permit increased concentrationof the trimethoxyboroxine in the epoxy resin, benzyl alcohol ispreferred. Benzyl alcohol is preferred because of its purity, as well asits index of refraction, its clear color, its high flash point, itsrelatively low solubility in water, its low viscosity, and its highboiling point.

Both the epoxy resins capable of serving as the matrix for the intenseheat-resistant composite and the trimethoxyboroxine and theirheat-resistant properties are known to those skilled in the art ofcomposite transparency production. However, it is the inclusion of thephenyl substituted alkyl alcohol which enables one to increase the levelof trimethoxyboroxine which results in an increase in intense heatresistance for the transparency not otherwise present. The phenylsubstituted alkyl alcohol is present in a concentration of from about 20parts to about 50 parts per one hundred parts of trimethoxyboroxine orfrom about 1 part to about 10 parts per 100 parts of epoxy resin.Preferably, the concentration of benzyl alcohol is 33 parts to onehundred parts of trimethoxyboroxine, or 3.3 parts to one hundred partsof epoxy resin.

Referring now to FIG. 1, it may be seen that the transparency composite,generally referred to as 10, is composed of three layers with the epoxyresin interply 20, a reaction product of an adduct of trimethoxyboroxineand benzyl alcohol with an epoxy resin placed between an inside ply 40and an outside ply 30. The outside ply 30 may be composed of transparentmaterials well known to those skilled in the art and specificallyproviding impact, ballistic, abrasion, weather resistant and lightreflectant resistant properties which resin interply 20 complements.

Typically, this outside ply 30 may be composed of acrylic,polycarbonate, polyurethane and any inside ply 40 may be chosen fromthose same transparent materials or others well known to those skilledin the art which are not necessary for impact, ballistic, abrasion,weather resistant or light reflection resistance.

All of the components of interply 20 are mixed and degassed, then castagainst an acrylic ply through the use of a casting cell technique wellknown to individuals in the industry. Should it be necessary to castinterply 20 by itself, the same technique can be used, the onlydifference being interply 20 would be cast against a chemically treatedglass plies, such that after cure the glass plies can be removed,resulting in an optically clear interply 20. This interply casting canthen be bonded to other transparent layers with materials as discussedbelow. However, the use of the alcohol permits larger castings thanpreviously possible. Gel times are increased by the addition of thealcohol to permit larger castings, as may be seen in FIG. 3.

When joining the various plies 20, 30 and 40 of the transparencycomposite 10, it may be necessary to use binding means to insureadequate contiguity between the various layers. For example, bindingmeans 45 may exist between the intense heat-resistant resin interply 20and inside ply 40, and this binding means 45 may be chosen fromadhesives such as silicones, urethanes and epoxies. Also, binding means35 may be necessary between intense heat-resistant resin interply 20 andoutside ply 30, the composition of such binding means being typicallysilicones, urethanes, and epoxies.

However, it is preferred to utilize a mercaptan resin for binding means35 and 45, as described below, to increase resistance to moisturepermeability for transparency composite 10.

The intense heat-resistant resin interply 20 may optionally be composedof an epoxy resin cured with adducts of a boroxine such astrimethoxyboroxine, phenyl substituted alkyl alcohols, and organicphosphorous compounds selected from the following formula: ##STR2##Where R₃ is selected from the group consisting of hydrocarbon radicalshaving from 1 to 24 carbon atoms, halo-substituted organic radicalshaving from 1 to 24 carbon atoms, and multihalo-substituted organicradicals having from 1 to 24 carbon atoms; and where R₃ may be the sameor different radicals.

The R₄ is selected from the group consisting of all the radicals of R₃,oxygen, and radicals of the formula: --O--R₆, where R₆ is selected fromthe group consisting of all the radicals of R₃, organo-phosphoruspolymeric radicals, and organo-phosphorus esters; where R₅ is selectedfrom the group consisting of hydrogen, hydroxyl, oxygen, sulfur,halogens or no radical at all; and where Z is selected from the groupconsisting of oxygen, sulfur, or no radical at all. Examples of R₃ arephenyl, alkyl-substituted phenyl, chloro-substituted alkyl, and alkylradicals. Examples of R₄ radicals are the examples of R₃ radicals,oxygen, phenoxy, alkyl-substituted phenoxy, alkoxy, alkyl-substitutedalkoxy, chloro-substituted phenoxy, chloro-substituted alkoxy radicalsand radicals having phosphorus units in polymeric or esterconfiguration.

Specific compounds include triphenyl phosphite, diphenyl phosphite,diphenyl isodecyl phosphite, tris nonylphenyl phosphite, tri(beta, beta'dichloroisopropyl) phosphate, tri(beta chloroethyl) phosphate, bischloroethyl phosphate ester, and a phosphate polymer of the formula:##STR3## where n is a number from 1 to 20.

The desirable phosphite compounds are: diphenyl phosphite,trisnonylphenyl phosphite, triphenyl phosphite, diphenylisodecylphosphite, diphenylisooctyl phosphite and phenyldiisodecyl phosphite.Preferably, diphenyl phosphite and triphenyl phosphite may be used. Theaddition of from 1 parts to 40 parts of an organic phosphorous compoundsuch as per 100 parts of the epoxy resin dramatically increases theintense heat-resistant properties of the interply 20 at hightemperatures, typically greater than 2000° F. Alternately, theconcentration of the organic phosphorus compound may be from about 50parts to 250 parts per 100 parts of the boroxine or from about 5 partsto about 40 parts per 100 parts of the epoxy resin. The addition of thisamount of triphenyl phosphite provides sufficient phosphorus in theresin to increase the time of burn-through of a 1/4 inch casting ofinterply 20 almost ten times as long as interply 20 without phosphorusis further beneficial by providing a greater than 20 percent increase intime of burning at the lower temperatures around 2000° F. Therefore, theinclusion of this phosphite significantly increases the intenseheat-resistant properties already present in the interlayer 20 andcomplements the other resistant properties in outer layer 30 in thetransparency composite 10.

Of the phosphate compounds, the specific phosphate compounds alreadymentioned are desirable. Preferably, tri(beta, beta' dichloroisopropyl)phosphate and tri(beta chloroethyl) phosphate may be used. The former iscommercially available under the trade name Fyrol FR-2 manufactured byStauffer Chemical Company, whereas the latter compound is commerciallyavailable as Fyrol CEF, manufactured by Stauffer Chemical Company. Theaddition of from about 10 parts to about 400 parts of the phosphatecompound per 100 parts of the boroxine compound or from about 1 part toabout 40 parts per 100 parts of the epoxy resin dramatically increasesthe intense heat-resistant properties of the interply 20, as seen inFIG. 15, at high temperatures, typically greater than 2000° F.

Alternately, the concentration of the phosphate compound may be fromabout 50 parts to 250 parts per 100 parts of the boroxine or from about5 parts to about 30 parts per 100 parts of the epoxy resin. The additionof this amount of the preferred chlorophosphate compounds describedabove provides sufficient phosphorus in the resin to increase the timeof burn-through of a casting of interply 20, as seen in FIG. 16 and thefollowing tables.

A comparison of the phosphate compound with the phosphite compounddemonstrates the preference of the phosphate compounds. In theproduction of the phosphite compounds, trace amounts of water areimpurities which generate the production of phenol during the curing ofthe interply 20. The generation of free phenol accelerates gel timeswhich must be retarded as seen in FIG. 4 to permit larger castings.Substitution of the phosphate compound for its synergisticheat-resistant properties into interply 20 avoids the presence of waterimpurities in the phosphite compounds, which permits a control over thegel time of the larger castings. Further, the phosphate compound doesnot shorten gel times because the chemical interaction of the phosphateduring curing does not produce byproducts which act as accelerators forthe reaction. As the optimum phosphate compound concentration isobtained, it may be possible to eliminate the phenol substituted alkylalcohol as an inhibitor of gel time, such as that seen in FIG. 3. Thefollowing Table 2 demonstrates the formulation of an interply 20employing phosphate compounds. However, it may be possible to employ acombination of phosphite and phosphate compounds for improvedburn-through efficiency.

                                      TABLE 2                                     __________________________________________________________________________    FORMULATIONS OF INTERPLY 20 USING PHOSPHITE                                   AND PHOSPHATE COMPOUNDS, RESPECTIVELY/IMPROVEMENT IN HEAT RESISTANCE                  1  2  3   4   5   6   7   8   9   10 11  12  13  14 15                __________________________________________________________________________    Boroxine                                                                              10 10 10  10  10  10  10  10  10  10 10  10  10  10 10                Compound                                                                      (triemethoxy-                                                                 boroxine)                                                                     Phenyl   3  3 3    3   3  3    3   3  3   -- --  --  --  -- --                Substituted                                                                   Alkyl Alcohol                                                                 (benzyl                                                                       alcohol)                                                                      Novalac-Type                                                                          90 90 90  45  45  45  --  --  --  -- --  --  --  -- --                Epoxy Resin                                                                   (DEN-431)                                                                     Bisphenol-F                                                                           -- -- --  45  45  45  90  90  90  90 90  90  90  90 90                Type                                                                          Epoxy Resin                                                                   (EPICLON-                                                                     830)                                                                          Phosphite                                                                             10 -- 5   10  --  5   10  --  5   -- --  --  --  -- --                Compound                                                                      (triphenyl                                                                    phosphite)                                                                    Phosphate                                                                             -- 10 5   --  10  5   --  10  5   -- 10  15  20  25 30                Compound                                                                      (Fyrol CEF)                                                                   Silane   1  1 1    1   1  1    1   1  1   -- --  --  --  -- --                Compound                                                                      (A-187)                                                                       Burn-through                                                                          1.6                                                                              1.6                                                                              1.5 1.9 1.9 1.8 2.4 2.2 2.0 2.0                                                                              3.0 3.0 3.0 2.0                                                                              2.0               time at                                                                       approximately                                                                 6000° F. (sec.)                                                        Percentage                                                                            con-                                                                             0% -6% +19%                                                                              +19%                                                                              +13%                                                                              +50%                                                                              +38%                                                                              +25%                                                                              con-                                                                             +50%                                                                              +50%                                                                              +50%                                                                              0% 0%                change  trol                              trol                                in heat                                                                       resistance                                                                    __________________________________________________________________________

As may be seen by reference to Table 2, variations of the formulations1-9 demonstrate the substitution of the phosphate compound in interply20 compared with a phosphite compound in interply 20. When coupled withthe reaction processing advantages of the phosphate compound, thesubstitution of the phosphate compound for the phosphite compound isdesirable. Therefore, the use of interply 20 having phosphate compoundstherein for any heat-resistant interlayer 20 in any laminate describedherein is possible and within the concept of this invention. Testing forformulations 1-9 for burn-through time at approximately 6000° F. wasconducted with a laminate structure identified in FIG. 15 where plies 30and 40 were acrylic.

An examination of formulations 10-15 in Table 2, in comparison with FIG.16 demonstrates the ability of an interply 20 having a phosphatecompound to resist the penetration of high heat sources. Formulations10-15 demonstrate an increasing concentration of the phosphate compoundfrom a control having no phosphate to an interply 20 having 30 parts byweight of phosphate compound. As seen in FIG. 16, three samples of eachformulation was exposed to a heat source developing temperatures atabout 6000° F. The reciprocal of penetration in inches demonstrates theresistance of each formulation to exposure time in seconds.Consequently, it is apparent that an optimal concentration of thephosphate ranges between about 10 parts by weight to about 20 parts byweight. Indeed, formulations 11-13 were capable of withstanding exposuretimes for a period of about three seconds which exceeds the burn-throughtime for any of the formulations 1-9. Therefore, it is optimal to havefrom about 10 to about 20 parts of the phosphate compound in interply20. Again, testing of interply 20 occurred using a laminate seen in FIG.15 where inside and outside plies 30 and 40 respectively, were bothacrylic.

Referring again to Table 2, it is also apparent that the epoxy resin maydesirably be a bisphenol-F type epoxy resin. Comparison of formulations1-3 with formulations 7-9 demonstrate a percentage change in heatresistance when the novalac-type epoxy resin is substituted with thebisphenol-F type epoxy resin.

Referring now to FIG. 2, the importance of intense heat-resistant epoxyresin interply 20 in a clad composite transparency may be understood.This transparency is shown cross-sectionally to demonstrate theeffectiveness of a particular clad composite format. Clad outside ply 30having binding means 35 is secured to intense heat-resistant resininterply 20 comprising an epoxy resin cured with adducts oftrimethoxyboroxine and benzyl alcohol alone or together with triphenylphosphite. Alternatively, interply 20 may be cured with a boroxinecompound and a phosphate compound, alone or together with aphenyl-substituted alcohol. A silicon interlayer 80 functions as aflexible adhesive to the opposite surface of interply 20 to a silicatelayer 70 typically composed of soda lime glass, borosilicate glass,aluminosilicate glass, silica glass or 96 percent silica glass. On theopposite side of silicate layer 70 is an interlayer 60 which consists ofa silicone or polyurethane or polyvinyl butyral interlayer. On theopposite side of interlayer 60 is a second silicate layer 70. On theopposite side of the second silicate is binding means 45 which consistsof a silicone or polyurethane interlayer. On the opposite side of thebinding means 45 is the inside ply 40 of the composite, composed of thesame materials as discussed above, including polycarbonate.

However, it is also possible to utilize a mercaptan resin for any or allof binding means 35 and 45 and interlayers 60 and 80. The importance ofsuch mercaptan resin in moisture permeability resistance for composite50 is described below.

It has been found that the combination of these layers 20, 30, 35, 40,45, 60, 70, and 80 in the order described above provides a synergisticresistance greater than the application of layers 30 and 40 surroundinginterlayer 20. Clad outer layer 30 may be selected from thosetransparent materials commonly known to those skilled in the art, asdescribed above and typically be acrylic.

For an understanding of the improved heat-resistant properties ofinterply 20, reference is had to FIG. 5.

                  TABLE 3                                                         ______________________________________                                        HEAT RESISTANT TRANSPARENCIES - RELATIONSHIP                                  BETWEEN BURNTHROUGH TIME AND                                                  EXPOSURE TEMPERATURE                                                                    Line                                                                          A       B       C         D                                         ______________________________________                                        Trimethoxyboroxine                                                                        7.5       10      10      7.5                                     Benzyl Alcohol                                                                            --        5       3       2.5                                     Triphenyl Phosphite                                                                       --        5       10      --                                      DER-332     100       --      --      --                                      DEN-431     --        85      90      90                                      Heloxy-68   --        15      --      --                                      Silane A-187                                                                              --        1       1       1                                       Diphenyl Phosphite                                                                        --        --      --      15                                      Burnthrough at                                                                            378       522     790     9000                                    2000° F. (secs.)                                                       Burnthrough at                                                                            0.4       3.0     3.7     5.8                                     6000° F. (secs.)                                                       ______________________________________                                    

It can be seen from FIG. 5 that by the addition of benzyl alcohol, ahigher concentration of trimethoxyboroxine can be incorporated,resulting in improved, burn-through resistance at 2000° F. and at 6000°F.

Transparencies 10 and 50 which contain interply 10 may be utilized invarious military and industrial applications. Typically, theseapplications may include the use of transparencies in military hardwareand aircraft, as well as spacecraft. Further, industrial applicationsinclude transparencies where protection against the thermal effects offossil fuel fires, nuclear blasts and high energy radiation arerequired.

The lasting success of any transparency composite, designed to withstandhigh heat resistance, impact resistance, ballistic resistance, abrasionresistance remains dependent upon its continuing transparent nature. Theplurality of layers of composites 10 and 50 and the chemical compositionof each layer are differentially susceptible to the permeation ofmoisture into and through the layers. The retention of moisture betweenand within the various layers of this invention and any conventionaltransparency composite having multiple layers creates a haze whichdisrupts clarity of light transmissions through the transparencycomposite.

A barrier to the generation of haze is necessary for any multi-layertransparency composite. The layers 35 and 45 and interlayers 60 and 80have been found to provide the most effective permeation barrier,resistant to moisture permeability into central layers, such asheat-resistant interlayer 20 and silicate layers 70 as seen in FIG. 1and FIG. 2, or for heat resistant interlayers 20 having phosphatecompounds therein.

The composition for the binding means 35 and 45 and interlayers 60 and80 comprises about 100 parts by weight of a mercaptan terminated resin,from about 40 to about 250 parts by weight of an epoxy resin, and fromabout 0.5 to about 4.0 parts by weight of a silane catalyst.

The mercaptan terminated resin is an aliphatic hydrocarbon basedcompound having a thio reactive group terminating each end of themolecule. The mercaptan has the following general formula: ##STR4##where R is an aliphatic hydrocarbon having from 1 to 18 carbon atoms andn is 1 or 2. The mercaptan resin is a material commercially availablefrom Diamond Shamrock Corporation and sold identified as DION-3-800LC.

The epoxy resin of the binding means 35 or 45 or interlayer 60 or 80 iscomposed of epoxy resins previously disclosed with reference to interply20. Typical epoxy resins include, but are not limited to, bisphenol-Atype, bisphenol-F type, and novolac type epoxy resins. A preferredconcentration of the epoxy resin depends on the type of epoxy resinused. For an epoxy-novolac type resin the preferred concentration isabout 100 parts by weight. Epoxy resins commercially available includeDER-332, a product of Dow Chemical Company.

The silane catalyst of the binding means 35 or 45 or interlayer 60 or 80is composed of an amine terminated silane compound such as

N-aminoalkyl-aminoalkyl-trialkoxysilanes of the formula ##STR5## whereinR₁ is an alkylene having 1-6 carbon atoms and R₂ is an alkyl, having 1-6carbon atoms, and

aminoalkyl-trialkoxysilanes of the formula ##STR6## wherein R₁ and R₂are as defined above.

Examples of preferred silanes are gamma aminopropyl triethoxy silane andnormal beta aminopropyl gamma aminopropyl trimethoxy silane. Thepreferred concentration of the amino-silane catalyst is about 2.5 partsby weight. The amino-silane is commercially available from Union Carbidein their A-1110 and A-1120 formulations.

As expressed above, the binding means 35 or 45 and interlayer 60 or 80have traditionally employed conventional silicones, urethanes, andepoxies. However, use of the mercaptan interlayer for these purposesprovides unexpected improvement to resistance to moisture permeation.The following table compares the test samples having various compositeconstructions, including a construction having outer ply 30,heat-resistant interlayer 20, binding means 45 and inner ply 40, such asthat seen in FIG. 11, and a construction having no binding means 35 or45.

                  TABLE 4                                                         ______________________________________                                        Composite                    Thick-                                           Number     Composite Component                                                                             ness (in.)                                       ______________________________________                                        1          polycarbonate (30)                                                                              0.256                                                       silicone resin (35)                                                                             0.1                                                         heat-resistant interlayer (20)                                                                  0.236                                                       silicone resin (45)                                                                             0.1                                                         polycarbonate (40)                                                                              0.256                                            2          polycarbonate heat-resistant 0.256                                            mercaptan interlayer (35)                                                                       0.1                                                         heat resistant interlayer (20)                                                                  0.236                                                       mercaptan interlayer (45)                                                                       0.1                                                         polycarbonate (40)                                                                              0.256                                            3          as-cast acrylic (30)                                                                            0.125                                                       heat-resistant interlayer (20)                                                                  0.236                                                       as-cast acrylic (40)                                                                            0.125                                            4          as-cast acrylic (30)                                                                            0.125                                                       heat-resistant interlayer (20)                                                                  0.236                                                       silicone resin (45)                                                                             0.1                                                         polycarbonate (40)                                                                              0.256                                            5          as-cast acrylic (30)                                                                            0.125                                                       heat-resistant interlayer (20)                                                                  0.236                                                       mercaptan layer (45)                                                                            0.1                                                         polycarbonate (40)                                                                              0.256                                            6          stretched acrylic (30)                                                                          0.1                                                         heat-resistant interlayer (20)                                                                  0.125                                                       stretched acrylic (40)                                                                          0.1                                              7          urethane (30)     0.1                                                         heat-resistant interlayer (20)                                                                  0.236                                                       urethane (40)     0.1                                              8          urethane (30)     0.1                                                         silicone resin (35)                                                                             0.1                                                         heat-resistant interlayer (20)                                                                  0.236                                                       silicone resin (45)                                                                             0.1                                                         urethane (40)     0.1                                              9          urethane (30)     0.1                                                         mercaptan interlayer (35)                                                                       0.1                                                         heat-resistant interlayer (20)                                                                  0.236                                                       mercaptan interlayer (45)                                                                       0.1                                                         urethane (40)     0.1                                              10         as-cast acrylic (30)                                                                            0.08                                                        heat-resistant interlayer (20)                                                                  0.236                                                       as-cast acrylic (40)                                                                            0.08                                             11         as-cast acrylic (30)                                                                            0.1                                                         silicone resin (35)                                                                             0.1                                                         heat-resistant interlayer (20)                                                                  0.236                                                       silicone resin (45)                                                                             0.1                                                         as-cast acrylic (40)                                                                            0.1                                              12         as-cast acrylic (30)                                                                            0.08                                                        mercaptan interlayer (35)                                                                       0.1                                                         heat-resistance interlayer (20)                                                                 0.236                                                       mercaptan interlayer (45)                                                                       0.1                                                         as-cast acrylic (40)                                                                            0.08                                             ______________________________________                                    

The composites of Table 4 were tested under extreme temperature andhumidity conditions. The direct comparison of the performance of themercaptan resin of the present invention and the preformance of theconventional silicone resin, or no binding means at all, may be seen inthe graphs of FIGS. 6-9.

In FIG. 6, the percent of haze occurring in the composite is comparedwith days of constant exposure of the composite at 200° F. and 100percent relative humidity. All other parameters constant, a directcomparison of composite No. 2 with the mercaptan interlayer of thepresent invention demonstrates the increased resistance to moisturepermeation in the latter composite. Likewise, a direct comparison ofcomposites No. 4 and No. 5 show the increased resistance to moisturepermeation in the latter composite. Composites No. 2 and No. 5 areclearly superior to their counterparts No. 1 and No. 4, as well as No. 3and No. 6 which do not provide any binding means moisture permeationprotection.

In FIG. 7, a graph showing the effect of constant exposure to 120° F.and 95 percent relative humidity to the same six composites is seen.While not as pronounced as that seen in FIG. 6, the comparison ofcomposites No. 1 and No. 2 and of composites No. 4 and No. 5 clearlyindicates the superiority of the mercaptan interlayer binding means overthe silicone resin binding means.

In FIG. 8, the graph showing the test of exposure at 200° F. and 100percent relative humidity for the remaining six composites is seen. Adirect comparison of composites No. 8 and No. 9, where the onlydifference is the substitution of mercaptan interlayer for siliconeresin, demonstrates the clear superiority of the mercaptan resin inresistance to haze as caused by moisture permeation. Further, acomparison of composites No. 11 and No. 12, substituting mercaptaninterlayer for silicone resin, demonstrates the superiority of themercaptan interlayer of the present invention over conventional bindingmeans.

FIG. 9 summarizes the superiority of the mercaptan interlayer of thepresent invention over conventional or no resin by comparing performanceat 200° F./100% relative humidity with performance at 120° F./95%relative humidity. At identical acceptable percentage haze levels, themercaptan interlayer could last as long as 100 days at 120° F./95%relative humidity and 35 days at 200° F./100% relative humidity. Bycomparison, the slicone resin could only withstand about 22 days at 120°F./95% relative humidity and 8 days at 200° F./100% relative humidity.

FIGS. 6-8 also demonstrate that the mercaptan interlayer of the presentinvention is effective for conventional outer and inner plies 30 and 40:acrylic, polycarbonate, urethane, and any combinations of them.Moreover, the mercaptan interlayer is available to replace theconventional silicone, epoxy, or urethane resins for any transparencycomposite using any conventional transparency including silicatescommonly known as glass. Indeed, the mercaptan interlayer of the presentinvention is an effective interlayer 60 and 80 for clad compositetransparency 50 as seen in FIG. 2.

Table 5 below demonstrates a comparison of the specific permeabilityvalues for various formulations of the mercaptan interlayer and theconventional silicone and other resins. The specific permeability of afilm to moisture is defined as the milligrams of water that permeate onesquare centimeter of film of 1 millimeter thickness each 24 hours aftera constant rate has been attained under the preferred conditions of 25°C. and using 100% relative humidity inside the cup and a phosphoruspentoxide desiccated atmosphere outside the cup. The formula ofcalculation is SP=W[T(25.4 mm/in)]/A where SP is specific permeability,W is weight loss in milligrams in a 24 hour period, T is the filmthickness in inches, and A is exposed cup surface area.

                  TABLE 5                                                         ______________________________________                                                         Film    Specific                                                              Thick-  Permeability.sup.4                                   Type of Resin    ness    (ASTM D-1632-62)                                     ______________________________________                                        mercaptan interlayer.sup.1                                                                     0.098   0.4978                                               mercaptan interlayer.sup.2                                                                     0.124   0.0627                                               mercaptan interlayer.sup.3                                                                     0.114   0.4633                                               low-strength silicone                                                                          0.100   4.8539                                               low-strength RTV sili-                                                        cone             0.104   4.2270                                               high-strength silicone                                                                         0.100   4.8768                                               high-strength RTV sili-                                                       cone             0.118   5.4549                                               pigmented RTV silicone                                                                         0.101   4.0020                                               ______________________________________                                         .sup.1 Mercaptan interlayer comprising 100 parts by weight of mercaptan       resin, 100 parts by weight of epoxy resin, and 2 parts by weight of silan     catalyst.                                                                     .sup.2 Mercaptan interlayer comprising 100 parts by weight of mercaptan       resin, 50 parts by weight of epoxy resin, and 1.5 parts by weight of          aminosilane catalyst.                                                         .sup.3 Mercaptan interlayer comprising 100 parts by weight of mercaptan       resin, 100 parts by weight of epoxy resin, and 1 part by weight of            aminosilane catalyst.                                                         .sup.4 Units in mg. mm/24 hr. cm.sup.2.                                  

Because the ideal specific permeability is near zero, it is readily seenthat a mercaptan interlayer of the present invention is approximately 10times better than conventional resins. This direct comparisondemonstrates the vast superiority of a mercaptan interlayer of thepresent invention over those binding agents presently employed.

Two other properties significant for the interlayer of the presentinvention are ultimate strength and modulus. During high temperature,high humidity condition, the interlayer must maintain proper adhesion toprevent delamination of the interlayer and the other various layers inthe composite. Further, the interlayer must have an acceptable rate ofchange of modulus during the high temperature, high humidity conditions,to prevent alteration of the interlayer effectiveness sandwiched betweenother layers during the course of use. For a comparison of modulus andultimate strength properties of the interlayers of the present inventionwith interlayers common to those skilled in the art, reference is had toTables 6 and 7. Table 6 describes the formulation of the testingmaterial and Table 7 demonstrates the effect of high temperature andhigh humidity on the modulus and ultimate strength properties of theformulations.

                  TABLE 6                                                         ______________________________________                                        FORMULATION OF INTERLAYER FOR COMPOSITE                                       OF GLASS - INTERLAYER - POLYCARBONATE                                                Mercap-                 High   Fumed                                   Formu- tan      Epoxy   Amino- Strength                                                                             Silica                                  lation Resin    Resin   Silane Silicone                                                                             Compound 1                              ______________________________________                                        1      100      100     2      --     --                                      2      100      150     2      --     --                                      3      100      175     2      --     --                                      4      100      200     3      --     --                                      5      --       --      --     100    5                                       6      --       --      --     100    --                                      ______________________________________                                         *1 A thixotropic agent available commercially as CABO-SIL EH5.           

                                      TABLE 7                                     __________________________________________________________________________             Torsional - Shear Modulus/Ultimate                                            Strength (PSI)                                                                Formulation                                                                   1    2   3    4    5   6                                             __________________________________________________________________________    Days of                                                                              1 210/771                                                                            78/148                                                                            25/62                                                                              28/60                                                                              25/43*                                                                            16/53                                         Exposure at                                                                          2 207/450                                                                            --  22   22    6/8**                                                                            --                                            120° F./95%                                                                   3 --   --  --   --   --  22/72                                         Relative                                                                             4 --   --  --   --   --    7/19**                                      Humidity                                                                             6 190/291                                                                            49/110                                                                            --   33/67                                                                              6/10                                                                              --                                                   7 --   --  33/65                                                                              --   --  --                                                   14                                                                              166/266                                                                            73/122                                                                            --    98/153                                                                            9/14                                                                              --                                                   15                                                                              --   --   55/101                                                                            --   --  --                                                   27                                                                               85/200                                                                            --  --   105/289                                                                            --  --                                            __________________________________________________________________________     *Haze Appeared                                                                **Delamination Started                                                   

As may be seen from an examination of Table 7, a variation in theformulation of the inner layer of the present invention may control themodulus and its rate of change during the days of exposure tohigh-temperature/high-humidity conditions. Over the course of the periodexamined, the ultimate strength and its rate of change could becontrolled by the type of formulation of the interlayer. Generally, withincreasing epoxy resin concentration, the modulus and ultimate strengthcomparisons during the days of the exposure increased when the epoxy wasgreater than 150 parts per 100 parts of mercaptan resin.

Table 7 also demonstrates the clear superiority of the interlayerformulations of the present invention over those interlayer compositionsknown to those skilled in the art. On the first day, formulation No. 5exhibited haze, and by the fourth day, both silicone formulationsstarted to delaminate from the composite ofglass-interlayer-polycarbonate. In comparison to this, the formulations1 and 4 lasted as long as 27 days when the experiment was concluded toreport these results. Furthermore, the interlayer formulations of thepresent invention have a variety of modulus and ultimate strengthproperties to meet various commercial applications depending upon thematerials between which the interlayer is sandwiched.

From an examination of FIGS. 13 and 14, it is possible to optimize theformulation for modulus stability and ultimate strength stability. FIG.13 demonstrates in graphic form the information shown in Table 6 for acomparison of initial modulus with the modulus after 14 days ofexposure. A ratio of epoxy resin/mercaptan resin exhibits stability overthe 14 days in the range of 1.5 to 1.8. Likewise, this ratio isconfirmed for ultimate strength comparisons as seen in FIG. 14.

The mercaptan composition of the present invention is effective, notonly to resist moisture permeation between plies of transparentcomposite construction. As seen in FIG. 10, edge sealant 95 may sealedges of outer ply 30, heat-resistant interlayer 20, binding means 45(either of the invented composition or a conventional composition) andthe upper surface of inner layer 40. The composite shown in FIG. 10 isthe same as the composite 90 shown in FIG. 11, typical of transparentcomposites used in high elevation aircraft. Edge sealer 95 is likewiseuseful to seal edges of composites as shown in FIG. 1 and 2 or anyconventional transparent composite, either with inner ply 40 extendingbeyond the other transparency components or cut at the same place as theother transparency components.

The mercaptan composition may also fill in the slot created during themanufacture of the transparency on the outside edge of any transparencycomposite. As seen in FIG. 12, this slot filler 105 combines thefunctions of the edge sealant 95 and the interlayer 45. Neither the slotfiller 105 nor the edge sealant need be transparent and may betranslucent or opaque with the addition of thixotropic agents, such asfumed silica compounds, or fillers. Indeed, slot filler 105 and edgesealer 95 may merge into a perimeter sealant.

The edge sealer 95 and the slot filler 105 demonstrates significantimprovements over the use of high-strength silicones known to thoseskilled in the art. An examination of Table 8 demonstrates the moistureimpermeability of the mercaptan compositions over that of thehigh-strength silicone.

                                      TABLE 8                                     __________________________________________________________________________    EXAMINATION OF GLASS-SILICONE-POLYCARBONATE COMPOSITES WITH                   EDGE SEALERS AND SLOT FILLERS EXPOSED 29 DAYS AT 120° F./95% R.H.      PANEL NO. 1       PANEL NO. 2                                                                             PANEL NO. 3                                                                              PANEL NO. 4                                                                             PANEL NO.                    __________________________________________________________________________                                                     5                            SLOT-     HIGH-STRENGTH SILICONE       MERCAPTAN*                                                                              MERCAPTAN**                  FILLER    PLUS 5% BY WT.               COMPOSITION                                                                             COMPOSITION                  (105)     CAB-O-SIL EH-5               PLUS 5% BY WT.                                                                          PLUS 5% BY WT.                         (Fumed Silica Compound)      CAB-O-SIL EH-5                                                                          CAB-O-SIL EH-5                                                      (Fumed Silica                                                                           (Fumed Silica Compound)                                             Compound)                              EDGE      NONE    MERCAPTAN MERCAPTAN  MERCAPTAN MERCAPTAN                    SEALER            COMPOSITION*                                                                            COMPOSITION**                                                                            COMPOSITION*                                                                            COMPOSITION**                (95)              PLUS 5% BY WT.                                                                          PLUS 5% BY WT.                                                                           PLUS 5% BY WT.                                                                          PLUS 5% BY WT.                                 CAB-O-SIL EH-5                                                                          CAB-O-SIL EH-5                                                                           CAB-O-SIL EH-5                                                                          CAB-O-SIL EH-5                                 (Fumed Silica                                                                           (Fumed Silica                                                                            (Fumed Silica                                                                           (Fumed Silica Compound)                        Compound) Compound)  Compound)                              INTERLAYER                                                                              Slot-Filler                                                                           Edge sealer cut                                                                         Edge sealer cut                                                                          Edge sealer cut                                                                         Edge sealer cut              (HIGH-    can be removed                                                                        off       off        off       off                          STRENGTH          Slot-Filler could                                                                       Slot-Filler could                                                                        Slot-Filler                                                                             Slot-Filler had              SILICONE)         be removed with                                                                         be removed with                                                                          could be removed                                                                        to be dug out                (45)              manual difficulty                                                                       difficulty with difficulty                                  Silicone inter-                                                                       Silicone inter-                                                                         Silicone inter-                                                                          Silicone inter-                                                                         Silicone inter-                        layer can be                                                                          layer could be                                                                          layer could be                                                                           layer appeared                                                                          layer appeared                         readily delam-                                                                        delaminated from                                                                        delaminated from                                                                         to be well                                                                              to be well                             inated from                                                                           both, The adhe-                                                                         glass only-was                                                                           bonded    bonded - minor                         glass and poly-                                                                       sion was much                                                                           better than Panel    spot delaminations                     carbonate                                                                             better than Panel                                                                       No. 1                                                               No. 1                                                       __________________________________________________________________________     *Mercaptan Resin 100 Epoxy Resin 100 AminoSilane 2                            **Mercaptan Resin 100 Epoxy Resin 200 AminoSilane 2                      

Each panel was subjected to 29 days of exposure at 120° F. and 95%relative humidity. Panel No. 1 only had a high-strength silicone slotfiller and once that was removed, it was apparent that the siliconeinterlayer could be readily delaminated from both the glass and thepolycarbonate layers. In contrast to this the mere addition of an edgesealer having one mercaptan composition plus the thixatropic agentincrease the performance of the composite during the 29 days ofexposure. After the edge sealer 95 was cut off, the slot filler 105could only be removed with manual difficulty. However, the siliconeinterlayer could be delaminated from both the glass and polycarbonate,although the adhesion was better than that found in Panel 1. Byincreasing the epoxy resin concentration, Panel 3 demonstrated someimprovement over that seen for Panel 2. In this case, after the edgesealer and slot filler were cut off and removed with manual difficulty,the silicone interlayer could be delaminated from only the glass layer.While Panels 2 and 3 represent improvement over the conventionalperformance of Panel 1, Panels 4 and 5 provide even greater improvement.

By using the mercaptan compositions for both slot filler 105 and edgesealer 95, the interlayer was significantly protected from moisturepermeation. For the interlayers of Panels 4 and 5, the combination ofthe edge sealer and slot filler provided the protection to maintain abond between the silicone interlayer and both the glass andpolycarbonate. Indeed, using this second mercaptan composition, slotfiller 105 had to be dug from the periphery of the Panel No. 5.

The mercaptan compositions of the present invention not only serve as aninterlayer, but also may serve as an edge sealer or slot filler. Thevariety of combinations of transparent composites which may employ thecomposition of the present invention in these various functions iswithin the scope of this invention.

According to the process of the present invention with regard to makinga haze-free, high transparent, high heat-resistant laminate, an initiallaminate is first made, generally indicated by the numeral 200. Thepurpose of this laminate as shown in FIG. 17, is to cast a highheat-resistant material therein as described hereinabove. That is, thehigh heat-resistant material generally contains a boroxine compound inan epoxy resin, as well as optionally various phosphites, phenylsubstituted alcohols, and the like. The laminate is assembled byproviding spacer blocks 202. On either side of spacer blocks 202 is aprotective non-glass layer, one of which is an as-cast acrylic layer orsheet 210. To each protectant layer 210 is added an ordinary orconventional glass sheet 220. The purpose of the glass sheet is toprevent the acrylic from flexing or bowing outwardly or inwardly, sinceglass is a relatively stiff and inflexible material. Thus, generally anynon-flexible material may be utilized in lieu of glass such as aluminumplates, and the like. Once the laminate has been formed, the highheat-resistant material is cast into place and allowed to cure. Aninitial laminate is formed, as shown in FIG. 17. Upon cure, the outerlayers of glass, etc., are removed providing a preform laminate having alayer of high heat-resistant material therein which is not exposed tothe air and hence moisture buildup on the heat-resistant surfaces isprevented. The preform, generally indicated by the numeral 230, thus hasat least one as-cast acrylic layer. Spacers 202 may remain intact or beremoved from subsequent use of the preform laminate.

As noted above, the high heat-resistant material which may be utilizedwith regard to various high heat sources such as fossil fuel fires,nuclear explosion, high energy lasers, or other high temperature heatsources, is generally made of a mixture of compounds such as epoxyresins, various boroxine compounds, various phosphorus compounds, andthe like. The ranges, desired amounts, preferred compounds, preparation,and all aspects thereof are all set forth hereinabove and is herebyfully incorporated. Once the high heat-resistant compound 205 has beencast, injection molded, or otherwise added to the space betweenprotectant layers 220, it is cured. Curing temperature can range fromroom or ambient temperature; that is, from about 60° to 70° F. toapproximately 250° F. A desirable temperature range is from about 150°F. to about 200° F., with approximately 190° F. being preferred.Actually, the upper limit of the curing temperature is the softeningpoint of the as-cast acrylic. Thus, depending upon the type of acrylic,the curing temperature can even exceed 250° F. Naturally, time of curewill generally vary inversely proportional to the curing temperature.Thus, room temperature cure will roughly range from about 18 to 24hours, whereas a cure at approximately 190° F. will roughly averageapproximately 3 hours.

The epoxy utilized in the high heat-resistant layer can generally be anytype of epoxy or novolac type epoxy resin. The only requirement is that,regardless of type of epoxy resin utilized, the amount of novolacstherein be approximately a minimum of 10 percent by weight, that is from10 percent to about 100 percent, and preferably from about 25 percent toabout 100 percent by weight.

It has been found that the high heat-resistant material gives relativelygood release when separated from the as-cast acrylic plastic layer.Accordingly, no release compounds are required as are required whenglass is utilized. The elimination of the various release compounds, forexample, Repcon, or dimethyldichlorosilane, largely eliminates any hazebuildup during the formation of the initial high heat-resistant laminateor during subsequent process steps.

With respect to protectant layer 210 being an acrylic layer, itgenerally can be any conventional acrylic "as-cast" layer. "As-cast" isa term of the art which generally refers to the production of an acrylicsheet via a casting process. It does not relate to or include astretched acrylic layer. Examples of conventional acrylic layers includePlex II UVA, an acrylic manufactured by Rohm and Haas, and the like.

In lieu of one of the as-cast acrylic layers, a non-glass transparentmaterial may be utilized. Specific examples include polycarbonate,polyurethane, and the like.

Once preformed high heat-resistant laminate 230 is desired to beutilized, one as-cast acrylic layer thereof or the sole as-cast acryliclayer thereof is peeled off in a continuous process, that is withoutstopping, so as not to leave a visual distortion line within highheat-resistant layer 205. The peeling can occur from room temperature upto below the softening point of the acrylic, for example about 250° F.The remaining preform of the high heat-resistant layer and the as-castacrylic layer or the transparent material attached thereto has very lowstress incorporated into the layers.

Preferably, immediately upon the removal of the sole or one of theas-cast acrylic layers as shown in FIG. 19, the remaining laminatestructure is formed into a semi-final laminate or structure wherein theexposed surface of the high heat-resistant layer is covered, or into afinal high heat-resistant laminate, a specific example of which isgenerally indicated by the numeral 240 in FIG. 20. The final laminate isprepared by inserting spacer plugs, not shown, in association withregard to the high heat-resistant layer 205, and inserting at leastanother transparent layer 218 thereover to form a cavity. The cavity isthen filled with a flexible adhesive or interlayer to adhere thetransparent layer to the high heat-resistant material. The laminate isthen cured.

Layers 205 and 210 of the final laminate have been previously described.The clear adhesive material layer 214 can be any conventionaltransparent material which acts as a barrier between dissimilarmaterials with regard to coefficient of thermal expansion so that highclarity is maintained. The flexible adhesive layer 214 thus adherestransparent layer 218, which can be a backing layer, to the preformedlaminate. The result is a highly transparent laminate having very littlehaze therein. Thus, it is seen that according to the present invention,a process is presented whereby a preformed laminate 230 containing ahigh heat-resistant layer with the high heat-resistant layer beingprotected against haze formation until it is finally incorporated into afinal laminate. The final laminate in having additional layersincorporated therein of generally any conventional transparent materialin any combination results in numerous different combinations, one ofwhich is shown in FIG. 20. Examples of various transparent materialsinclude glass, acrylic, polyurethane, polycarbonate, transparentadhesives, and the like. Of course, any desired number of interlayersand transparent material layers can be utilized in any combination, inaddition to the preform layers so that numerous multi-layeredlaminations exist.

Layer 218 which often can be a backing layer can generally be anyconventional strong transparent material. Specific examples include anyconventional polycarbonate, as-cast acrylic, any conventionaltransparent polyurethane, and to a lesser desired extent, glass.Naturally, the thicknesses of any of the layers described in thisprocess can vary and, depending upon desired use, end results, and thelike.

As noted, the transparent adhesive layer resides on the highheat-resistant layer, according to the present invention, whenever itbonds materials of dissimilar coefficient of thermal expansion to reducestress and improve adhesion or moisture resistance. Naturally, more thanone transparent adhesive layer can be utilized in the laminate.Interlayer 214 can be any flexible adhesive as set forth above such asconventional silicone or polyurethane adhesive, or a mercaptan layer.The mercaptan adhesive will usually have an epoxy resin and a silanecatalyst as set forth above. The polyurethane and the mercaptan arepreferred since they do not require a primer coating.

Although any flexible transparent adhesive can be utilized which can becured from about room temperature up to about 250° F., or below thesoftening point of the acrylic layer, it is highly desirable that theacrylic not be distorted. Therefore, the use of a transparent adhesivehaving a low cure temperature as possible is desired. The lowtemperature also reduces any stress buildup in the laminate upon curethereof. Accordingly, the use of materials having cure temperatures ofless than 130° F. are preferred. Examples of specific clear adhesiveinterlayers 250 are set forth in the specification.

Other highly transparent, low haze, heat-resistant laminates can beformed utilizing the process of the present invention, with thefollowing flow diagram and specific examples representing only a portionof the numerous various possible combinations. ##STR7##

Should a primer be required, although the use of a primer is generallyavoided, any conventional primer such as a silicone primer can beutilized. The primer is cured at a temperature of from about roomtemperature to about 250° F. Desirably, a clear silicone priming agentis utilized to obtain adhesion between a heat-resistant layer and theinterlayer 214, or between the interlayer and the transparent material,and the like. Naturally, the time of cure will generally vary with thetemperature. In addition to a silicone primer, various specific types ofurethanes which prevent moisture penetration and to not result in hazebuildup may be utilized. In order to prevent any haze buildup during theprimary application, short cure times are desired.

The various layers can be cast flat as shown in the Figures or they canbe cast in a curved shape to produce the final item, for example acanopy for a jet fighter. The present invention is particularly suitablewith regard to forming curved laminates since protective layers 210 canbe readily formed whereas if a glass layer is used, it would requirespecial molds and high temperatures. Moreover, it is noted that incertain instances, a laminate is not required. Therefore, bothprotective sheets 210 as shown in FIG. 18 can be peeled off, and theitem utilized as for a window, as for example in a commercial jetaircraft. Since the window will be flat, it is highly rigid and requiresbending or stretching as does curved shapes. The monolithic sheet may becured in the protective layers. Alternately, it may be removed from theprotective layers and cured at temperatures above the 250° F., above theapproximate softening temperature of the as-cast acrylic.

Thus, according to the present process, a method is presented wherebyvarious high heat-resistant laminates can be formed whenever a flexibletransparent adhesive layer or inner liner layer is required to bepositioned and attached to the high heat-resistant layer and low haze isdesired. In use, upon the application of intense heat, the highheat-resistant layer which contains boroxane as well as other compoundsset forth herein will generally char and prevent the heat from beingtransferred to the remaining layers. The result is that the integrity ofthe laminate is maintained and that it is not totally burned away.

The improvement of the present invention is shown in the followingexamples which show lower haze values for various laminates madeaccording to the present process as compared to a different process.

EXAMPLE

A laminate was made according to FIG. 17 wherein as-cast acrylic layerswere positioned on either side of spacer blocks, and a glass plate waspositioned on either side thereof. To this construction was added aheat-resistant material having the formulation set forth in Table 3,Formulation C. The laminate was heated at 190° F. and allowed to curefor three hours. The glass sheets were removed from the laminate toyield a preform which was hung overnight. The next day one of theas-cast acrylic plies was removed at room temperature. The exposed highheat-resistant surface was mirror-like in appearance. Said surface waswiped with methanol to remove any dust therefrom. A silicone primermanufactured by General Electric, Type SS-4120, was flow-coated over thesurface and cured at 190° F. for one hour. Then, a sheet of likewiseprimed polycarbonate was placed over the prime surface in space relationtherefrom and a conventional silicone material added to the space toform an interlayer. The laminate which is similar in layers to FIG. 20,was cured for 13/4 hours at 190° F. The resultant laminate measured 4.1on a haze meter, but visually was very clear in appearance throughout.

Utilizing the same process, a chlorosilaned glass which had been coatedwith Repcon was made. This exact same identical laminate, with theexception of having a glass layer on the heat-resistant material wheninitially formed, had an average haze meter reading of from 5 to 6percent. From a visual standpoint, this laminate had a ghost patternthereon, that is appeared occluded and was visually varied difference inclarity from the above-noted laminate made utilizing the presentinvention.

Thus, as apparent from the Example, applicant's process results in avery marketedly improved clarity concerning the formation of highheat-resistant laminates.

While in accordance with the patent statutes, a best mode and preferredembodiments of the invention have been provided, the invention is not tobe limited thereto or thereby. Therefore, for an understanding of thescope of the invention, reference is had to the following claims.

What is claimed is:
 1. A process for preparing a transparent, low haze,high heat-resistant laminate, comprising the steps of:forming a highheat-resistant layer between transparent protective layers so that atransparent protective layer is located on either side of saidheat-resistant layer, at least one of said protective layers being anas-cast acrylic layer, and curing said heat-resistant layer at atemperature of from about 60° F. to about 250° F., wherein said highheat-resistant layer has from about 80 parts to about 100 parts byweight of an epoxy resin, said epoxy resin containing at least 25percent by weight of novolac therein, and from about 5 to about 30 partsby weight of a boroxine compound having the formula ##STR8## wherein Ris a group having from 1 to 18 carbon atoms, and from about 1 part toabout 10 parts by weight of a phenyl substituted alkyl alcohol, saidalkyl alcohol having from 1 to 10 carbon atoms.
 2. A process accordingto claim 1, wherein when only one of said layers is an as-cast acryliclayer said protective layer other than said as-cast acrylic layer is amaterial selected from the group consisting of an as-cast acrylic, apolyurethane, a polycarbonate, and combinations thereof.
 3. A processaccording to claim 2, including the step of removing at least one ofsaid acrylic layers.
 4. A process according to claim 3, includingapplying a primer to said high heat-resistant layer, and curing saidprimer layer from an ambient temperature to about 250° F.
 5. A processaccording to claim 3, including applying a transparent layer to saidhigh heat-resistant layer.
 6. A process according to claim 3, includingadding a flexible adhesive interlayer to said high heat-resistant layer.7. A process according to claim 6, including adding a transparent layerto said flexible adhesive layer, and curing said adhesive layer at atemperature of from about ambient to about 250° F.
 8. A processaccording to claim 7, wherein said transparent material is selected fromthe group consisting of polycarbonate, polyurethane, glass, as-castacrylic, and combinations thereof wherein said flexible adhesive layeris a silicone adhesive, a polyurethane adhesive, or a mercaptanadhesive, and curing said heat resistant layer at a temperature of fromabout 150° F. to about 200° F.
 9. A process according to claim 3,including locating a transparent material in spaced relationship to saidhigh heat-resistant layer, and subsequently adding a flexible adhesiveto said space between said heat-resistant layer and said transparentlayer.
 10. A process according to claim 9, wherein said transparentmaterial is selected from the group consisting of polycarbonate,polyurethane, glass, as-cast acrylic, and combinations thereof.
 11. Aprocess according to claim 10, wherein said flexible adhesive isselected from the group consisting of a silicone adhesive, apolyurethane adhesive, a mercaptan adhesive, and combinations thereof.12. A process according to claim 11, including curing said flexibleadhesive at a temperature ranging from about ambient temperature toabout 250° F. and curing said heat-resistant layer at a temperature offrom about 150° F. to about 200° F.
 13. A process according to claim 3,including removing both of said protective layers.
 14. A processaccording to claim 3, including adding a plurality of flexible adhesivelayers and a plurality of transparent layers to said heat-resistantlayer, one of said adhesive layers located on said heat-resistant layer.15. A process according to claim 13, including adding a plurality offlexible adhesive layers and a plurality of transparent layers to saidheat-resistant layer, one of said adhesive layers located on saidheat-resistant layer, and curing said adhesive layer at a temperature offrom ambient to about 250° F.
 16. A process according to claim 1, 2, 7,8, 9, 12, or 15 wherein said high heat-resistant layer contains fromabout 1 to about 40 parts by weight per 100 parts of said epoxy compoundof an organic phosphorus compound having the formula ##STR9## where R₃is selected from the group consisting of hydrocarbon radicals havingfrom 1 to 24 carbon atoms, halo-substituted organic radicals having from1 to 24 carbon atoms, and multihalo-substituted organic radicals havingfrom 1 to 24 carbon atoms; and where R₃ may be the same or differentradicals,where R₄ is selected from the group consisting of all theradicals of R₃, oxygen, and radicals of the formula: --O--R₆, where R₆is selected from the group consisting of all the radicals of R₃,organo-phosphorus polymeric radicals, and organo-phosphorus esters;where R₅ is selected from the group consisting of hydrogen, hydroxy,oxygen, sulfur, halogens or no radical at all; and where Z is selectedfrom the group consisting of oxygen, sulfur, or no radical at all.
 17. Aprocess according to claim 16, wherein said boroxine has an alkyl grouphaving from 1 to 5 carbon atoms, wherein said alkyl of said alcohol hasfrom 1 to 10 carbon atoms, and wherein said phosphorus compound isselected from the group consisting of diphenyl phosphite, triphenylphosphite, trisnonylphenyl phosphite, diphenylisooctyl phosphite,diphenylisodecyl phosphite, and combinations thereof.
 18. A processaccording to claim 17, wherein said boroxane compound istrimethoxyboroxine, wherein said alcohol is benzyl alcohol, and whereinsaid phosphorus compound is selected from the group consisting ofdiphenyl phosphite, triphenyl phosphite, and combinations thereof.
 19. Aprocess according to claim 5, 7, 8, 9, or 12, wherein said interlayer isan epoxy resin containing a mercaptan, said inner layer comprising about100 parts by weight of a mercaptan compound having the formula ##STR10##wherein R is an aliphatic hydrocarbon group having from 1 to 18 carbonatoms, and wherein n is 1 or 2, from about 40 to about 250 parts byweight of an epoxy resin having at least 10 percent by weight of novolactherein, and from about 0.5 parts by weight to about 4.0 parts by weightof a silane selected from the group consisting of:N-aminoalkyl-aminoalkyl-trialkoxysilanes of the formula: ##STR11##wherein R₁ is an alkylene having from 1 to 6 carbon atoms and R₂ is analkyl having 1 to 6 carbon atoms, and aminoalkyl-trialkoxysilanes of theformula: ##STR12## wherein R₁ and R₂ are as defined above, andcombinations thereof.
 20. A process according to claim 16, wherein saidinterlayer is an epoxy resin containing a mercaptan, said inner layercomprising about 100 parts by weight of a mercaptan compound having theformula ##STR13## wherein R is an aliphatic hydrocarbon group havingfrom 1 to 18 carbon atoms, and wherein n is 1 or 2, from about 40 toabout 250 parts by weight of an epoxy resin having at least 10 percentby weight of novolac therein, and from about 0.5 parts by weight toabout 4.0 parts by weight of a silane selected from the group consistingof: N-aminoalkyl-aminoalkyl-trialkoxysilanes of the formula: ##STR14##wherein R₁ is an alkylene having from 1 to 6 carbon atoms and R₂ is analkyl having 1 to 6 carbon atoms, and aminoalkyl-trialkoxysilanes of theformula: ##STR15## wherein R₁ and R₂ are as defined above, andcombinations thereof.
 21. A process according to claim 18, wherein saidinterlayer is an epoxy resin containing a mercaptan, said inner layercomprising about 100 parts by weight of a mercaptan compound having theformula ##STR16## wherein R is an aliphatic hydrocarbon group havingfrom 1 to 18 carbon atoms, and wherein n is 1 or 2, from about 40 toabout 250 parts by weight of an epoxy resin having at least 10 percentby weight of novolac therein, and from about 0.5 parts by weight toabout 4.0 parts by weight of a silane selected from the group consistingof: N-aminoalkyl-aminoalkyl-trialkoxysilanes of the formula: ##STR17##wherein R₁ is an alkylene having from 1 to 6 carbon atoms and R₂ is analkyl having 1 to 6 carbon atoms, and aminoalkyl-trialkoxysilanes of theformula: ##STR18## wherein R₁ and R₂ are as defined above, andcombinations thereof.
 22. A process for preparing a transparent, lowhaze, heat-resistant laminate, comprising the steps of:locating twoprotective layers in juxtaposition to one another and having a spacetherebetween, at least one of said protective layers being an as-castacrylic material, forming a high heat-resistant material between saidspaced protective layers, and curing said heat-resistant material at atemperature of from about 60° F. to about 250° F., said highheat-resistant layer having from about 80 parts to about 100 parts byweight of an epoxy resin, said epoxy resin containing at least 25percent by weight of novolac therein, and from about 5 to about 30 partsby weight of a boroxine compound having the formula ##STR19## where R isa group having from 1 to 18 carbon atoms, and from about 1 to about 40parts by weight of a phosphate compound.
 23. A process according toclaim 22, wherein when only one of said layers is an as-cast acryliclayer, said protective layer other than said as-cast acrylic layer is amaterial selected from the group consisting of an as-cast acrylic, apolyurethane, a polycarbonate, and combinations thereof.
 24. A processaccording to claim 23, including the step of removing one of saidacrylic protective layers and exposing a surface of said heat-resistantlayer.
 25. A process according to claim 24, including the step ofpriming said exposed surface of said high heat-resistant layer andcuring said primers at a temperature of from about ambient to about 250°F.
 26. A process according to claim 24, including the step of adding aflexible adhesive to said high heat-resistant layer, and curing saidadhesive agent at a temperature of from ambient to about 250° F.
 27. Aprocess according to claim 26, including adding a transparent layer tosaid flexible adhesive layer.
 28. A process according to claim 27,including curing said heat-resistant layer at a temperature of fromabout 150° F. to about 200° F.
 29. A process according to claim 28,wherein said transparent material is selected from the group consistingof polycarbonate, polyurethane, glass, as-cast acrylic, and combinationsthereof, and wherein said flexible adhesive layer is a siliconeadhesive, a polyurethane adhesive, or a mercaptan adhesive.
 30. Aprocess according to claim 22, 24, 27, 28, or 29, wherein said phosphateis selected from the group consisting of tri(beta, beta'dichloroisopropyl) phosphate, tri(beta chloroethyl) phosphate, bischloroethyl phosphate ester, and a phosphate polymer of the formula:##STR20## where n is a number from 1 to
 20. 31. A process according toclaim 30, wherein said interlayer is an epoxy resin containing amercaptan, said inner layer comprising about 100 parts by weight of amercaptan compound having the formula ##STR21## wherein R is analiphatic hydrocarbon group having from 1 to 18 carbon atoms, andwherein n is 1 or 2, from about 40 to about 250 parts by weight of anepoxy resin having at least 10 percent by weight of novolac therein, andfrom about 0.5 parts by weight to about 4.0 parts by weight of a silaneselected from the group consisting of:N-aminoalkyl-aminoalkyl-trialkoxysilanes of the formula: ##STR22##wherein R₁ is an alkylene having from 1 to 6 carbon atoms and R₂ is analkyl having 1 to 6 carbon atoms, and aminoalkyl-trialkoxysilanes of theformula: ##STR23## wherein R₁ and R₂ are as defined above, andcombinations thereof.
 32. A process according to claim 30, wherein saidboroxine compound is trimethoxyboroxine, and wherein said phosphatecompound is selected from the group consisting of tri(beta, beta'dichloroisopropyl) phosphate, and tri(beta chloroethyl) phosphate.